Document EP1143539 discloses a panel of this type; the cells of this panel include an organic electroluminescent layer in equilibrium with the atmosphere of the sealed space. Since this electroluminescent layer is organic, it is particularly sensitive to any trace of oxygen and/or water vapour in this space. Oxygen and/or water vapour disturb and degrade the constituent materials of the organic electroluminescent layer, especially its light emission capabilities, reducing the quality of the display and/or the lifetime of the panel.
In that document, the front plate (Ref. 12 in FIG. 4 of the document) serves as substrate for the electroluminescent layer, and the absorbent agent (Ref. 50 in FIG. 4 of the document) is distributed uniformly over the surface of the rear plate, which serves as the external part of the casing. Since the emitted light passes through the substrate, this type of cell is usually termed “back-emitting”. In contrast, the prior art discloses panels whose cells are turned “top-emitting”, which means that the emitted light passes not through the substrate but, on the contrary, through the plate on the opposite side from the substrate. In this case, the presence of an absorbent agent on this opposite plate, as in document EP 1 143 539, would impede the passage of the emitted light and would greatly reduce the luminous efficiency of the panel.
Document US 2002-060654 discloses a back-emitting panel in which the absorbent agent, instead of being distributed uniformly over the surface of the rear plate as in EP1 143 539, is distributed in grooves distributed over the entire surface of this rear plate; such a solution again does not solve the question of the distribution of the absorbent agent in top-emitting panels.
Finally, documents U.S. Pat. No. 5,239,228 and JP 2002-050471 disclose top-emitting electroluminescent panels whose transparent front plate includes a single groove around the perimeter, which groove is placed away from the active or emitting surface, and which contains an absorbent agent. The drawback of such a solution is that it does not ensure sufficiently homogenous distribution of the absorbent agent over the entire surface of the panel, this being particularly prejudicial in the case of large panels such as those with a diagonal that exceeds 20 cm.